1. Field of the Invention
The present invention relates to a liquid droplet jetting apparatus which discharges liquid droplets, and a nozzle plate which is used in the liquid droplet jetting apparatus.
2. Description of the Related Art
An ink-jet head which discharges ink from nozzles onto a recording paper is available as a liquid-droplet jetting apparatus which discharges or jets liquid droplets. In this ink-jet head, pressure is applied to the ink by various kinds of actuators and the ink is discharged from the nozzles. Then, after the discharge of the ink, the ink is drawn in the nozzles because the pressure in ink channels connected to the nozzles is decreased. However, after the discharge of the ink, when the ink is not completely drawn into the nozzles and a portion or part of the ink is adhered to an ink discharge surface on which ejecting ports of the nozzles are formed, during a subsequent ink discharge, an amount of ink discharged and a direction of discharge are varied in some cases and there is a possibility that the print quality is degraded. In view of this, in a general ink-jet head, a water repellent treatment is performed on the ink discharge surface so that the ink is hardly adhered around the ejecting port of the nozzle.
However, only by performing the water repellent treatment on the ink discharge surface, it is difficult to prevent completely the ink from adhering in the vicinity of the ejecting port of the nozzle. For example, when a viscosity of the ink is decreased due to a rise in the temperature, a large amount of ink is overflowed or outflowed from the nozzle to the ink discharge surface. The outflowed ink moves freely on the ink discharge surface and there is a possibility that a part of the ink moving freely is accumulated or remains around the ejecting port of the nozzle. In view of this, an ink-jet head which is capable of preventing the accumulation of the ink around the ejecting port of the nozzle even when the ink is adhered to the ink discharge surface is proposed.
For example, in an ink-jet head described in U.S. Patent Application Publications No. US 2002/140774 A1 and No. US 2004/196332A1 corresponding to Japanese Patent Application Laid-open No. 2002-292877, a first area which is concentric with the ejecting port is provided around the ejecting port of the nozzle, and a second area having a liquid repellent property lower than a liquid repellent property of the first area is provided at an area other than the first area. Therefore, the ink adhered to the first area around the ejecting port of the nozzle is moved to the second area having the liquid repellent property lower than the liquid repellent quality of the first area, and the ink is hardly accumulated or remains around the ejecting port.